The North American beaver (Castor canadensis) is the continent’s largest rodent and one of the world’s most recognizable ecosystem engineers. This semi-aquatic mammal is renowned for its tireless dam-building activities, which dramatically reshape waterways and create wetland habitats. The beaver’s ability to fell trees and construct complex lodges often leads people to question the nature of its diet.
The Herbivorous Classification
The simple answer to whether beavers are omnivores is no; they are classified as herbivores, consuming a diet composed entirely of plant matter. Herbivores obtain their energy solely from vegetation, unlike carnivores or omnivores. The beaver’s entire biological structure, from its specialized teeth to its gut, is tuned to process plant materials.
Primary Plant Food Sources
A common misconception is that beavers eat the hard, woody part of the trees they fell. In reality, they primarily seek out the cambium, the soft, nutrient-rich layer found just beneath the outer bark. This inner bark provides necessary starches and sugars, especially during winter when other food sources are scarce. Beavers select specific deciduous trees for their diet, favoring species such as aspen, willow, cottonwood, and birch.
Seasonal variations dictate the rest of the beaver’s menu throughout the year. During spring and summer, their diet shifts to include a wide variety of softer, highly digestible vegetation. They consume aquatic plants like water lilies and cattails, along with roots, rhizomes, leaves, and grasses found near the water’s edge. The felled branches and logs are typically used for construction or stored underwater as a winter food cache.
Specialized Adaptations for Digestion
The beaver’s ability to subsist on a tough, fibrous diet is supported by two biological adaptations. The most visible of these are their large, continuously growing incisors, which are hardened on the front surface with iron compounds. This iron gives the teeth their characteristic orange color and creates a self-sharpening edge as the softer dentin on the back wears away faster. These chisel-like teeth are suited for stripping bark and cutting down woody stems.
Internally, the beaver possesses a digestive system specialized for breaking down cellulose, the main component of plant cell walls. Like other monogastric herbivores, they employ a process called hindgut fermentation. This occurs in an enlarged pouch called the cecum, located at the junction of the small and large intestines. The cecum acts as a fermentation chamber where symbiotic bacteria and fungi produce enzymes that break down complex cellulose molecules into usable nutrients.